Anthrax spores were first produced as weapons in the 1950s. Several countries including the former Soviet Union, the United States and Iraq are known to have produced anthrax weapons. Anthrax is a particularly fearsome biological warfare agent, not only because of its deadliness, but also because anthrax weapons are relatively easy to produce and deliver. Production of anthrax spores requires little more than basic laboratory equipment and growth media. Anthrax weapons may be comprised of an anthrax source and an industrial sprayer that can produce aerosol particles of the appropriate size for victims to inhale. Such sprayers, for instance, can be mounted on low flying airplanes or other vehicles and used to spread anthrax over a wide area. Because of the ease and relatively small expense involved in producing and delivering anthrax weapons, such weapons are potentially highly attractive weapons of mass destruction for terrorist groups. Thus, in addition to potential organized military conflicts that may give rise to the use of such weapons, terrorist organizations are a potential threat for the use of such weapons in airports, office buildings and other centers of human activity.
Anthrax is caused by B. anthracis, a gram-positive, sporulating bacillus. B. anthracis is a soil bacterium and is distributed worldwide. The organism exists in the infected host as a vegetative bacillus and in the environment as a spore. The anthrax spore is typically the infective form of the bacterial life cycle. Anthrax spores can survive adverse environmental conditions and can remain viable for decades. Animals such as cattle, sheep, goats and horses can contract the spores while grazing. Humans can contract anthrax from inoculation of minor skin lesions with spores from infected animals, their hides, wool or other products, such as infected meat (Franz et al. (1997) J. Am. Med. Assoc. 278(5): 399-411).
The typical mode of entry of the anthrax spore into the body, inhalation, results in an illness known as woolsorter's disease. After deposit in the lower respiratory tract, spores are phagocytized by tissue macrophages and transported to hilar and mediastinal lymph nodes. The spores germinate into vegetative bacilli, producing a necrotizing hemorrhagic mediastinitis (Franz et al., supra). Symptoms include fever, malaise and fatigue, which can easily be confused with the flu. The disease may progress to an abrupt onset of severe respiratory distress with dyspnea, stridor, diaphoresis and cyanosis. Death usually follows within 24 to 36 hours.
Cutaneous anthrax infection occurs following external contact with anthrax. In cutaneous anthrax infection, symptoms include a skin infection that is distinguished by a raised itchy bump that resembles an insect bite in the first days and develops into a vesicle and then ulcer with a characteristic black necrotic area in the center. 20% of untreated cases of cutaneous infection result in death.
Gastrointestinal anthrax infection follows consumption of contaminated meat. Symptoms include nausea, loss of appetite, vomiting, fever, abdominal pain, vomiting of blood and severe diarrhea. Death results in 25%-60% of cases.
Because the effects of exposure to anthrax are not immediate, and because the initial symptoms are easily confused with the flu, there is a need for a fast method to detect B. anthracis in a subject. This need is enhanced by the increasing number of anthrax threats that are called into governmental authorities each year and the recent transport of anthrax through the United States Postal System. A fast method for determining whether a subject has been infected with anthrax is, therefore, essential.
Anthrax spores have S-layers, as do spores of many other archea and bacteria. Most S-layers are comprised of repeats of a single protein (Etienne-Toumelin et al., J. Bacteriol. 177:614-20 (1995)). The S-layer of B. anthracis, however, is comprised of at least two proteins: EA1 (Mesnage et al., Molec. Microbiol. 23:1147-55 (1997)) and surface array protein (SAP) (see Etienne-Toumelin, et al., supra). Fully virulent B. anthracis isolates are encapsulated by a capsule that encompasses the S-layer of the bacteria and prevents access of antibodies to both EA1 and SAP (Mesnage et al., J. Bacteriol. 180:52-58 (1998)). Amino acids 180 to 700 of SEQ ID NO:1 are specific for SAP.
A fast and efficient method is needed to detect infection of animals, and especially humans, by anthrax. The present invention addresses this and other problems.